This invention relates to radar signal processing. In particular, this invention concerns Doppler processing and clutter filtering on irregular Pulse Repetition Time (PRT) sampled signal.
In conventional radar, Doppler processing uses discrete Fourier transform (DFT) on regularly sampled signals because the pulse repetition time is constant within a burst. So, such conventional processing using discrete Fourier transform (DFT) is not applicable to irregular Pulse Repetition Time (PRT) sampled signal.
Irregular Pulse Repetition Time (PRT) is usually meant to prevent blind speeds (velocity ambiguity), the jammers from locking on the radar""s Pulse Repetition Time (PRT), and also to solve Doppler ambiguities.
Current work on irregular sampling is mostly motivated by image processing. Efficient algorithms based on frame operations have been developed as xe2x80x9cEfficient numerical methods in non-uniform sampling theoryxe2x80x9d written by Feichtinger, H. G. and al in Numerische Mathematik 69 (NUHAG). Wavelet transform in digital filter banks as xe2x80x9cMultirate systems and filter banksxe2x80x9d written by Vaidyanathan, P. P. Prentice-Hall Publishers (1993) illustrates efficient 1D applications with irregular samples obtained by integer decimation or expansion of uniform samples.
In Doppler radar signal processing, Pulse Repetition Time (PRT) staggering has been studied, but with emphasis on the Fourier analysis, rather than on solving the irregular-sampling problem.
An exception is the NSSL algorithm proposed in the American patent U.S. Pat. No. 6,081,221 for Doppler weather radar. This NSSL algorithm offers a non-ambiguous solution in Doppler speed and does only ground clutter filtering. Such ground clutter has a mean frequency equal to zero because it does not move. So, clutter with any mean frequency like: sea clutter or rain clutter . . . can not be filtered with this proposed NSSL algorithm.
This invention solves the above-mentioned drawbacks, in particular solving the velocity ambiguity and filtering any type of clutter, providing a deconvolution method which filter any kind of clutter even varying clutter like sea clutter, rain clutter . . .
An object of this invention is a deconvolution method of irregular pulse repetition time sampled signal x(tm), which comprises the following steps:
[S1] conversion of the irregular samples x(tm) to regular samples r(iTxcex5);
[S2] computation of the spectrum dft(r) of these regular samples;
[S3] isolation of the clutter spectra in dft(r) by assuming clutter spreads over more than a few range gates;
[S4] estimation of the clutter spectral lines from the mean and the width of the isolated clutter spectra;
[S5] subtraction of the estimated clutter spectra from the total spectrum dft(r);
[S6] deconvolution of the remaining spectra.
In a first embodiment of the deconvolution method, the computation in the steps of subtraction [S5] and deconvolution [S6] is adjusted to the clutter type by the clutter spectra given by step [S3].
A further object of this invention is deconvolution system of irregular pulse repetition time sampled signal x(tm), which comprises:
Mean for converting the irregular samples x(tm) to regular samples r(iTxcex5);
Mean for computing the spectrum dft(r) of these regular samples;
Mean for isolating the clutter spectra in dft(r) by assuming clutter spreads over more than a few range gates;
Mean for estimating the clutter spectral lines from the mean and the width of the isolated clutter spectra;
Mean for subtracting the estimated clutter spectra from the total spectrum dft(r);
Mean for deconvolving of the remaining spectra.
Moreover, another object of this invention is the use of such deconvolution method in radar system.
A further object to this invention is the use of such deconvolution method as clutter filtering, in particular as sea clutter filtering.